In a radio receiver, a radio frequency (RF) signal is typically received using an antenna and the received RF is then processed along the receive path to recover the original signal transmitted. In the receive path, the received signal is subject to various processing such as amplifying, filtering, down-converting, demodulating, and etc. In a real radio environment, there are many un-intended signals which may interfere with an intended signal if the un-intended signals are not properly processed. By using a tuning filter is one effective means to block un-intended signals to ensure the quality of final received signal. In a radio transmitter, it also provides some advantage to use a tuning filter to suppress out-of-band signals which may be generated un-intentionally through the transmit path. Consequently, a tuning filter is widely used in radio receivers and also used in radio transmitters.
There are cases that a receiver has to receive signals in various frequency bands. For example, for a terrestrial broadcast TV receiver, the tuning circuit has to support TV channels in the low VHF band (such as 44-92 MHz in the US), the high VHF band (such as 167-230 MHz in the US) and the UHF band (for example, 470-860 MHz in the US). In practice, the tunable range of a tuning circuit is less than 20% of the carrier frequency so that the design requirements will not be too stringent. When the tunable range is beyond 20% of the carrier frequency, it will make the design more challenging. One common way to circumvent the issue of designing a tuning circuit with a very wide tuning-range is to use multiple tuning circuits so that the tuning range for each tuning filter can be effectively reduced.
A tuning circuit often comprises an adjustable capacitance device and other components such as inductors and resistors. A common practice in the field of integrated circuit is to use a switched capacitor array (SCA) as the adjustable capacitance device. The SCA usually comprises an array of capacitors connected in parallel where each capacitor is controlled by a respective switch to connect or disconnect the capacitor to or from the array. Therefore, the capacitance of the SCA can be digitally controlled by applying control signals to the switches. The SCA usually will take up a sizable silicon area. Multiple tuning circuits imply multiple SCAs needed. Therefore, it is very desirable to provide a system and method for multiple tuning circuits to share the SCA.